Share-Based Compensation - Summary of SAR Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
SARs
Shares, Granted		0	0
Stock Appreciation Rights (SARs)
SARs
Shares, Outstanding at beginning of year	1,292,142	1,402,784	1,535,804
Shares, Granted	332,159	195,560	326,811
Shares, Exercised	(179,702)	(267,077)	(376,673)
Shares, Forfeited	(45,441)	(38,738)	(80,515)
Shares, Expired	(1,547)	(387)	(2,643)
Shares, Outstanding at end of period	1,397,611	1,292,142	1,402,784
Shares, Exercisable at end of period	736,075	586,344	520,426
Weighted-Average Exercise Price, Outstanding at beginning of year	$ 42.20	$ 36.36	$ 31.66
Weighted-Average Exercise Price, Granted	107.31	74.59	46.13
Weighted-Average Exercise Price, Exercised	40.71	34.03	25.44
Weighted-Average Exercise Price, Forfeited	75.26	50.57	37.54
Weighted-Average Exercise Price, Expired	47.11	46.07	33.70
Weighted-Average Exercise Price, Outstanding at end of year	56.78	42.20	36.36
Weighted-Average Exercise Price, Exercisable at end of year	$ 35.90	$ 33.03	$ 30.51
Intrinsic value of exercised SARs	$ 11	$ 11	$ 8